关于Mapper.xml生效的问题

昨天在新建Springboot启动后，发现执行相关的SQL报错 org.apache.ibatis.binding.BindingException: Invalid bound statement，具体报错信息如下：

 org.apache.ibatis.binding.BindingException: Invalid bound statement (not found): com.hqtc.live.admin.common.dao.UserDao.list
     at org.apache.ibatis.binding.MapperMethod$SqlCommand.<init>(MapperMethod.java:227)
     at org.apache.ibatis.binding.MapperMethod.<init>(MapperMethod.java:49)
     at org.apache.ibatis.binding.MapperProxy.cachedMapperMethod(MapperProxy.java:65)
     at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:58)
     at com.sun.proxy.$Proxy89.list(Unknown Source)
     at com.hqtc.live.admin.common.service.impl.UserServiceImpl.list(UserServiceImpl.java:47)
     at com.hqtc.live.admin.common.service.impl.UserServiceImpl$$FastClassBySpringCGLIB$$eed42660.invoke(<generated>)
     at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
     at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:738)
     at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)
     at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:99)
     at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:282)
     at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96)
     at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
     at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:673)
     at com.hqtc.live.admin.common.service.impl.UserServiceImpl$$EnhancerBySpringCGLIB$$137fcb94.list(<generated>)
     at com.hqtc.live.admin.common.shiro.UserRealm.doGetAuthenticationInfo(UserRealm.java:46)
     at org.apache.shiro.realm.AuthenticatingRealm.getAuthenticationInfo(AuthenticatingRealm.java:568)
     at org.apache.shiro.authc.pam.ModularRealmAuthenticator.doSingleRealmAuthentication(ModularRealmAuthenticator.java:180)
     at org.apache.shiro.authc.pam.ModularRealmAuthenticator.doAuthenticate(ModularRealmAuthenticator.java:267)
     at org.apache.shiro.authc.AbstractAuthenticator.authenticate(AbstractAuthenticator.java:198)
     at org.apache.shiro.mgt.AuthenticatingSecurityManager.authenticate(AuthenticatingSecurityManager.java:106)
     at org.apache.shiro.mgt.DefaultSecurityManager.login(DefaultSecurityManager.java:270)
     at org.apache.shiro.subject.support.DelegatingSubject.login(DelegatingSubject.java:256)
     at org.apache.shiro.web.filter.authc.AuthenticatingFilter.executeLogin(AuthenticatingFilter.java:53)
     at org.apache.shiro.web.filter.authc.FormAuthenticationFilter.onAccessDenied(FormAuthenticationFilter.java:154)
     at org.apache.shiro.web.filter.AccessControlFilter.onAccessDenied(AccessControlFilter.java:133)
     at org.apache.shiro.web.filter.AccessControlFilter.onPreHandle(AccessControlFilter.java:162)
     at org.apache.shiro.web.filter.PathMatchingFilter.isFilterChainContinued(PathMatchingFilter.java:203)
     at org.apache.shiro.web.filter.PathMatchingFilter.preHandle(PathMatchingFilter.java:178)
     at org.apache.shiro.web.servlet.AdviceFilter.doFilterInternal(AdviceFilter.java:131)
     at org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125)
     at org.apache.shiro.web.servlet.ProxiedFilterChain.doFilter(ProxiedFilterChain.java:66)
     at org.apache.shiro.web.servlet.AbstractShiroFilter.executeChain(AbstractShiroFilter.java:449)
     at org.apache.shiro.web.servlet.AbstractShiroFilter$1.call(AbstractShiroFilter.java:365)
     at org.apache.shiro.subject.support.SubjectCallable.doCall(SubjectCallable.java:90)
     at org.apache.shiro.subject.support.SubjectCallable.call(SubjectCallable.java:83)
     at org.apache.shiro.subject.support.DelegatingSubject.execute(DelegatingSubject.java:383)
     at org.apache.shiro.web.servlet.AbstractShiroFilter.doFilterInternal(AbstractShiroFilter.java:362)
     at org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125)
     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
     at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99)
     at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
     at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:108)
     at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
     at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:81)
     at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
     at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197)
     at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
     at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199)
     at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
     at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:478)
     at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
     at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
     at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
     at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
     at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803)
     at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
     at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)
     at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459)
     at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
     at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
     at java.lang.Thread.run(Thread.java:745)

我在网上找了好多相关的blog，好多说是

　　1：Mapper.xml中的namespace不对应和mapper接口不对应

　　2：Mapper.xml中的方法(即id)和mapper接口中的方法名字不同或对应的方法不存在

　　3：返回类型不匹配(即没有正确配置ResultMap或者ResultType)

　　4：可能xml文件有缓存或者修改后没保存

　　5：可能没有配置MapperScan导致dao方法没有被扫描注入

　　6：配置文件中mybatis.mapper-locations或mybatis.typeAliasesPackage配置不正确

我逐条对比测试，发现不是上述的这些问题，那么问题出在哪里呢？

通过报错信息的第二行，我找到了MapperMethod.SqlCommand方法，具体代码如下：

     public SqlCommand(Configuration configuration, Class<?> mapperInterface, Method method) {
       final String methodName = method.getName();
       final Class<?> declaringClass = method.getDeclaringClass();
       MappedStatement ms = resolveMappedStatement(mapperInterface, methodName, declaringClass,
           configuration);
       if (ms == null) {
         if (method.getAnnotation(Flush.class) != null) {
           name = null;
           type = SqlCommandType.FLUSH;
         } else {
           throw new BindingException("Invalid bound statement (not found): "
               + mapperInterface.getName() + "." + methodName);
         }
       } else {
         name = ms.getId();
         type = ms.getSqlCommandType();
         if (type == SqlCommandType.UNKNOWN) {
           throw new BindingException("Unknown execution method for: " + name);
         }
       }
     }

通过分析我们得出进入了ms==null的逻辑，因此我们分析MapperMethod.resolveMappedStatement这个方法，看为什么这个sql对应的MappedStatement为什么为空，分析其代码如下

     private MappedStatement resolveMappedStatement(Class<?> mapperInterface, String methodName,
         Class<?> declaringClass, Configuration configuration) {
       String statementId = mapperInterface.getName() + "." + methodName;
       if (configuration.hasStatement(statementId)) {
         return configuration.getMappedStatement(statementId);
       } else if (mapperInterface.equals(declaringClass)) {
         return null;
       }
       for (Class<?> superInterface : mapperInterface.getInterfaces()) {
         if (declaringClass.isAssignableFrom(superInterface)) {
           MappedStatement ms = resolveMappedStatement(superInterface, methodName,
               declaringClass, configuration);
           if (ms != null) {
             return ms;
           }
         }
       }
       return null;
     }
   }

其中configuration.hasStatement(statementId)会判断有没有这个sql对应的方法。分析发现，org.apache.ibatis.session.Configuration方法中的属性 mappedStatements 为空。这就不难解释为什么报找不到方法的错误了。

那么为什么mappedStatements为空呢，我怀疑是mybatis.mapper-locations属性没有被正确加载解析，导致无法正确的找到每个接口方法对应的sql，那么接下来分析mybatis.mapper-locations有没有被加载。Mybatis相关的配置信息被加载后都存在MybatisProperties类中，通过调试查看这个类的属性发现，mybatis.mapper-locations已经被加载了。那么接下来看有没有被解析。我们找到了MybatisAutoConfiguration.sqlSessionFactory方法，具体代码如下：

   @Bean
   @ConditionalOnMissingBean
   public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception {
     SqlSessionFactoryBean factory = new SqlSessionFactoryBean();
     factory.setDataSource(dataSource);
     factory.setVfs(SpringBootVFS.class);
     if (StringUtils.hasText(this.properties.getConfigLocation())) {
       factory.setConfigLocation(this.resourceLoader.getResource(this.properties.getConfigLocation()));
     }
     Configuration configuration = this.properties.getConfiguration();
     if (configuration == null && !StringUtils.hasText(this.properties.getConfigLocation())) {
       configuration = new Configuration();
     }
     if (configuration != null && !CollectionUtils.isEmpty(this.configurationCustomizers)) {
       for (ConfigurationCustomizer customizer : this.configurationCustomizers) {
         customizer.customize(configuration);
       }
     }
     factory.setConfiguration(configuration);
     if (this.properties.getConfigurationProperties() != null) {
       factory.setConfigurationProperties(this.properties.getConfigurationProperties());
     }
     if (!ObjectUtils.isEmpty(this.interceptors)) {
       factory.setPlugins(this.interceptors);
     }
     if (this.databaseIdProvider != null) {
       factory.setDatabaseIdProvider(this.databaseIdProvider);
     }
     if (StringUtils.hasLength(this.properties.getTypeAliasesPackage())) {
       factory.setTypeAliasesPackage(this.properties.getTypeAliasesPackage());
     }
     if (StringUtils.hasLength(this.properties.getTypeHandlersPackage())) {
       factory.setTypeHandlersPackage(this.properties.getTypeHandlersPackage());
     }
     if (!ObjectUtils.isEmpty(this.properties.resolveMapperLocations())) {
       factory.setMapperLocations(this.properties.resolveMapperLocations());
     }

     return factory.getObject();
   }

在最后你是不是看到了

 if (!ObjectUtils.isEmpty(this.properties.resolveMapperLocations())) {
       factory.setMapperLocations(this.properties.resolveMapperLocations());
     }

按道理来说，这个方法是被@Bean注解修饰的，应该会被Spring自动注入，一单被自动注入，那么相应的会执行这个方法。但是通过调试发现，这个方法没有被执行，难怪mybatis.mapper-locations属性没有被正确解析。我突然想到，我们当时在做mysql主从的时候，在相关的配置类中自定义过 SqlSessionFactory 的实现和注入，有可能是这个问题。那么我尝试将我们自定义的SqlSessionFactory的实现给注释掉，重启后发现问题解决了。我们看下 MybatisAutoConfiguration 中关于 sqlSessionFactory 的注入代码部分如下：

@Bean
@ConditionalOnMissingBean
public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception {

我们看到了 @ConditionalOnMissingBean 这个注解，它的意思是如果BeanFactory中存在了 SqlSessionFactory，就不再注入当前的 SqlSessionFactory。这也就是我们自定义SqlSessionFactory的注入方法后，就不在执行这个注入代码的原因。

最后发现其实问题很简单，就是我们自定义的SqlSessionFactory 的注入覆盖了mybatis内部的注入方法，导致mybatis.mapper-locations没有被解析生效。

最后总结：

1：重视报错信息，通过报错信息我们往往能分析到问题产生的直接原因。

2：找到问题间的关联。就像上述问题，如果你熟悉mybatis的源码，你可能会很快的找到根本原因。如果你不熟悉源码，可以通过断点调试等方法，找到相关类和方法间的引用关系从而找到问题的关键。

3：还是多看看mybatis的源码吧。